Microbial Keratitis: Causes, Symptoms, and Treatment

Introduction 

There are many people in the world who are affected with problems related to their vision and most seek medical assistance for the same. However, this is not the only reason as to why people seek to wear contact lenses, rather, there are those who prefer the lenses for their aesthetic value. For people with genuine vision problems, they have sought various eye corrective measures. The use of Contact lenses is one of these methods that is used on a global scale. The Introduction of contact lenses proved to be a revolutionary step for the medical industry where more people, with the use of Contact Lenses (CL), can correct their vision. In the whole world, there is an estimated 125 million people who are contact wearers, be it for vision correction or aesthetic value. The industry has widely grown due to its popularity all over the world. More people are giving up on the spectacles as a means for vision correction and adapting Contact lenses. Researchers have, however, identified that contact wearers have a higher risk of contracting Microbial keratitis, an acute disease where the corneal tissue is invaded by replicating microbes (Keay & Stapleton 2008). The following report papers details Microbial Keratitis offering information on the disease, signs and symptoms, diagnosis, treatment options with their contradictions and any expected complications. 

Background 

Microbial keratitis is a rare disease that is caused due to a complication arising from the use of Contact Lens (CL) wear. It is a potentially blinding corneal infection that occurs very rarely for normal eyes (Stapleton & Carnt 2012). It is severely damaging if not detected in the earlier stages and only 50% of eyes have been found to recover full visuals when treatment is delayed (Wong et.al. 2012). It is a condition whereby a person experiences an inflammation that causes a disruption in the corneal epithelium and stroma. This inflammation causes a tear in the epithelial layer in order to inflict damage on the cornea. The Corneal Epithelium is a self-renewing, stratified epithelial sheet which acts as the front line of defence against attacking pathogens and also provides a smooth reflective surface that is essential for vision (Robertson, 2013). On Normal occasions in the absence of contact lens, ad any pre-existing ocular traumas, it maintains a very high and insurmountable defence against pathogenic microorganisms. In this way, it maintains a high defence against the attack from any antimicrobial proteins and surfactants that may be present in tear fluids while still maintain the inherent self-defence properties and characteristics of an epithelium layer (Robertson, 2013). 

There are many types of bacteria that can cause Microbial Keratitis infection, these include; Staphylococcus species, Pseudomonas aeruginosa, Streptococcus species and enteric gram-negative rods. These bacteria can be contracted through the following risk factors; dry eyes caused by Sjogren syndrome, Steven-Johnson syndrome, vitamin deficiency, prolonged corneal exposure from ectropion, Lagophthalmos and Entropion and Trichiasis that results in corneal defects. There are some other risk factors that can lead to the development of keratitis, these can be, chronic alcoholism, severe malnutrition, immunosuppressive drug use, immunodeficiency syndromes and malignancy. These conditions can impair the immune defence mechanisms that are currently in place leading to the contraction of opportunistic diseases (Schlossberg 2008). 

Risk Factors 

Depending on the type of Contact Lenses used, there are different risks associated with each use. Due to the presence of several types of contact lens liquid used, the risk percentages for various contacts variates depending on the liquid used. For Silicone Hydrogel and Hydrogel lenses, the risk of infections is 1 among 500 wearers of contact lenses per year, whereas for those who wear daily disposable contact lenses, the risk of infection was not lower compared to other types. However, the risk factors that highly increased the probability of infection included; smoking, poor hygiene, omission of handwashing before contact with Contact Lenses, lack of or infrequent case-cleaning and general poor hygiene. Also the amount of time one spends time wearing contact lenses was also a factor to consider based on the research of risk factors. Prolonged use of Contact Lens (can be overnight) per week poses a high risk factor of attaining Microbial keratitis (Stapleton & Carnt, 2012). 

Differential Diagnosis 

Microbial Keratitis early stage symptoms greatly resemble those of contact lens induced peripheral ulcer (CLPU). The determination of whether an infection is due to Microbial Keratitis of CLPU is based on the clinical judgement as no microbiologic or histopathologic investigations are done in order to determine the difference. However, the early MK is more severe and acute compared to CLPU frequently resulting in errors or misjudgement. There is also a similarity between Peripheral Unlcerative keratitis, Mooren’s Ulcer, Corneal Abrasion, Vernal keratoconjunctivitis with shield ulcer, sterile corneal foreign body, staphylococcal hypersensitivity and hypoxic or toxic corneal irritation. Each of these conditions possesses similar signs and symptoms, however, differentiating investigations that include negative cultures for corneal scraping, laboratory tests that provide evidence of underlying disorder to separate Ulcerative Keratitis, and diagnosis exclusion can be conducted to determine which of these the cause of infection is. For MK, the signs and symptoms are as follows; abrupt pain in the eye, reduced or unclear vision, increased levels of sensitivity to light, excessive production of tears and a discharge emanating from the eyes, redness of the eyes, photophobia and blurry vision. There is also the presence of white or yellowish infiltrates in the corneal stroma with signs of inflammation (Upadhyay, Srinivasan, & Whitcher, 2015). 

Diagnosis 

When diagnosing MK, having a historical record of the patient is important so as to eliminate the presence of contraction of other eye infections. Enquiring on whether the patient acquired an injury, the date and time, and help sought following the injury with the treatment offered is important. Enquiries onto the medical history of the patient, whether there has been a history of conjunctivitis in the family tree and such is also required. 

An examination should be conducted in order to properly identify the extent or symptoms of the infection. Examinations tests checking on; visual acuity for both the affected and unaffected eye should be recorded with or without glasses; an examination of the cornea through the use of a slit lamp microscope if available, fluorescein dye, either in a sterile strip or a sterile solution in order to determine which parts of the cornea have lost the epithelium. The solution shines bright green when viewed under a blue light effectively identifying which part of the cornea has lost the epithelium. During the examination, also look into the presence of the following signs in order to determine whether the eye is responsive to treatment; eyelid abnormalities such as trichiasis and lagopthalmos, reduced corneal sensation, conjunctival inflammation and discharge, corneal epithelial defects relating to size and shape, corneal inflammatory infiltrate relating to size and shape, thinning or perforation of the cornea and hypopyon. Also, for lesions that are greater thean 2mm in diameter, a corneal scrape sample should be acquired for microbiological analysis where possible (Upadhyay et al., 2015). 

Treatment Options 

There are three levels of treatment offered to patients depending on the stage at which the MK has reached. At the primary level, a patient should be referred to the nearest secondary or district eye centre. The patient should be put on antibiotic drops or ointment for the time being before they arrive at the centre. The patients should also be instructed against using traditional forms of medication. They should not be; given systemic antibiotics, issued with steroid drops and/or ointment and told to routinely patch the eye as it is not helpful, can be dangerous and is not required respectively. 

Where a test has been conducted and no fungal elements have been identified, thus eliminating Fungal keratitis, fortified cefazolin (50mg/mL) is issued 1 droop per hour, or Vancomycin (50mg/Ml). In the event it is not possible to administer eye drops, then a subconjunctival injection should be issued. Where fungal elements have been seen on microscopy, or fungal Keratitis is suspected, freshly reconstituted amphotericin-B 0.15% eye drops are issued hourly. Antibiotics may not be a good prescription as they may be harmful. 

Other adjunctive treatment includes, atropine 1% or homatropine 2% to be used twice a day in order to dilate the pupil. This is necessary to relive pain and prevent synechiae. Oral analgesics also help relieve the pain. In the event that intraocular pain is high, anti-glaucoma medication can be issued. Vitamin A supplements are also helpful where Vitamin A deficiency is prevalent. If the ulcer is responsive to treatment, the therapy should be continued for 2 or 3 weeks. If there is no response after the initial phase of treatment, then other methods, inclusive of surgery can be placed on the table. 

Contraindications and complications including pregnancy and children 

In pregnant women, the benefits of using the medication must be weighed against the potential risks to the infant. The drugs that are safe for patients may be unsafe for infants. Oral antibiotics that are harmful to the infant are to be avoided, however, extensive research should be conducted in order to ensure there is no harm done to the patient. 

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